Apparatus for fabricating a display device

ABSTRACT

Apparatus for fabricating a display device includes a stage capable of mounting an insulating substrate of the display device and moving the insulating substrate, linear scales which detect a position or moving distance of the substrate, a laser oscillator which generates continuous-waves laser light, a modulator which turns ON/OFF the continuous-wave laser light, a beam forming optic which shapes the continuous-wave laser light passing through the modulator into a linear or rectangular form, an objective lens which projects the at least one of the laser light on the insulating substrate so as to irradiate the insulating substrate with the laser light. The controller counts signals generated by the linear scales for every movement of the stage for a given distance, causes the modulator to turn the generated continuous-wave laser light in an ON state at time when a position of the insulating substrate on which the laser light irradiation is to be started reaches an area on which the laser light is projected, and causes the modulator to turn the generated continuous-wave laser light in an OFF state at another time.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 10/628,421, filedJul. 29, 2003. This application relates to and claims priority fromJapanese Patent Application No. 2002-256533, filed on Sep. 2, 2002 andNo. 2003-062938, filed on Mar. 10, 2003. The entirety of the contentsand subject matter of all of the above is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flat panel display device, and inparticular, to a display device using an insulating substrate withactive elements formed in a band-like polycrystalline semiconductorfilm, obtained by reforming an amorphous or granular polycrystallinesemiconductor film formed on the top surface of the insulating substrateso as to expand crystal grains into a substantially band-like shape byuse of annealing with laser light (also referred to merely as laserhereinafter) irradiated thereto to, a process of fabricating the same,and an apparatus for fabricating the same.

2. Description of Related Art

This type of display device comprises a multitude of data lines (drainlines for thin-film transistors) juxtaposed so as to be extended in adirection of the display region of an insulating substrate on one side(hereinafter referred to also as an active matrix substrate, and as athin-film transistor substrate in the case where thin-film transistorsare used as the active elements), with active elements such as thin-filmtransistors, thin-film diodes, and so forth, formed thereon, a multitudeof scanning lines (gate lines for thin-film transistors) juxtaposed soas to be extended in another direction crossing the direction describedas above, active elements formed of a granular polycrystalline siliconfilm (polysilicon film) as a semiconductor film formed on the activematrix substrate and disposed at cross-over points of the data lines andthe scanning lines, and pixels arranged in a matrix form, made up ofpixel circuits having pixel electrodes driven by the active elements,respectively. There will be described hereinafter mainly of a displaydevice using a silicon film as the semiconductor film and thin-filmtransistors, which are typical active elements, as the active elements.

With a flat panel display device of the present day, pixel circuitscomprising thin-film transistors, respectively, are made up of anon-crystalline silicon film (hereinafter referred to also as amorphoussilicon film) and a granular polycrystalline silicon film (hereinafterreferred to also as polysilicon film) as a semiconductor film on top ofan insulating substrate, made of glass, fused glass, etc., serving as anactive matrix substrate, and pixels are selected by switching of therespective thin-film transistors of the pixel circuits, thereby formingimages.

The thin-film transistor constituting each of the pixel circuits isdriven by a driving circuit (hereinafter referred to also as drivercircuit or driver) mounted on the periphery of the active matrixsubstrate. The granular polycrystalline silicon film described above isa silicon film which crystal grains are small in diameter as will bedescribed later. Herein, “crystal grains are small in diameter” means asize so small that, for example, there exist a multitude of grainboundaries of silicon crystals in an active layer (or active region) ofthe thin-film transistor, that is, within a so-called channel width,thereby causing current passing through the active layer to cut acrossthe multitude of the grain boundaries of the silicon crystals withoutfail.

If it becomes possible to form the driver circuit for driving thethin-film transistors of the pixel circuits concurrently with thethin-film transistors of the pixel circuits, drastic reduction inproduction cost and enhancement in reliability can be expected. However,because the conventional polysilicon film, which is a semiconductorlayer for forming the active layer of the thin-film transistor, has poorcrystallinity (crystal grains are small in grain size), operationperformance (operation characteristic) represented by mobility ofelectrons or holes is low, so that it is difficult to fabricate acircuit of which high-speed and high function are required. In order tofabricate the circuit having high-speed and high function, high-mobilitythin-film transistors are required, but to implement this, there is theneed for improving the crystallinity of the polysilicon film.Improvement on the crystallinity means primarily expansion of the grainsize of the crystal grains or rendering a dimension in one direction ofthe crystal grains to be greater than a dimension thereof, in otherdirections, so as to be turned into a band-like or stripe like shape,thereby increasing the dimensions thereof. Herein, to differentiate fromthe conventional polysilicon film, the silicon film as reformed isreferred to a band-like polysilicon film.

As a method for improving the crystallinity of a polysilicon film, therehas since been known annealing with laser light such as excimer laser,and so forth. With this method, by irradiating, for example, excimerlaser to an amorphous silicon film formed on top of an insulatingsubstrate (also referred to merely as a substrate hereinafter), made ofglass, fused glass, etc., the amorphous silicon film is turned into apolysilicon film, thereby improving the mobility. However, thepolysilicon film obtained by irradiation with the excimer laser is onthe order of several 100 nm in grain size, and the mobility thereof ison the order of 100 cm²/Vs, so that the performance thereof isinsufficient for use in the driver circuit for driving a liquid crystalpanel.

As a method of overcoming the problem, annealing techniques with the useof continuous-wave laser as described in Non-patent Document 1. PatentDocument 1 has description to the effect that by maintaining the pulsewidth of pulse laser light in a range of 1 μs to 100 ms, it is possibleto reduce fluctuation in threshold value of transistor fabricated.Further, description concerning reformation of a silicon film byirradiation of laser light is given in Patent Document 2.

[Non-patent Document 1]

-   F. Takeuchi et al “Performance of poly-Si TFTs fabricated by a    Stable Scanning CW Laser Crystallization” AM-LCD '01 (TFT4-3)    [Patent Document 1]-   JP-A No. 335547/1995    [Patent Document 2]-   JP-A No. 283356/1993

SUMMARY OF THE INVENTION

With the conventional techniques described in [Non-patent Document 1]described, by scanning the second harmonics of LD (laser diode) pumpedYVO₄ continuous wave laser on an amorphous silicon film formed on thesurface of a glass substrate to thereby cause growth of crystal grainsto occur, mobility in excess of 500 cm²/Vs was obtained. If mobility atthis level is achieved, a driver circuit high in performance can beformed and a so-called system on panel (or chip on glass: COG) mountingcan be implemented.

However, according to the conventional techniques described in[Non-patent Document 1], irradiation is performed by scanning the wholesurface of a region on the substrate, for forming a driver circuit, withthe continuous wave laser, and no consideration is given to an idea ofirradiation of necessary parts only. Accordingly, a wide regionincluding a part with high mobility where the driver circuit is formedand the periphery thereof is continuous irradiated. As a result, afterstart of laser irradiation, laser absorbed by a silicon film isconverted into heat, and accumulated in the substrate, so that thesilicon melts and undergoes aggregation by the agency of interfacialtension or thermal damage occurs to the substrate. In order to solve theproblem, it is sufficient to selectively irradiate laser light tonecessary regions only. Since irradiation is applied to specific spotson the substrate being moved at a high speed relative to laser, meansfor implementing laser irradiation start and stoppage with highprecision have not been known so far. So, this has been one the pendingproblems.

Further, in [Patent Document 1], it has been disclosed that fluctuationin the threshold value of a transistor produced by setting a pulse widthof pulse laser light to a range of 1 to 100 μs.

However, no thought has been given to a method of irradiating laserlight to a specific spot on a substrate being moved at a high speedrelative to laser. This has been another problem to be solved.

The present invention has been developed in view of the problemdescribed as above, and a fist object of the invention is to provide adisplay device comprising an active matrix substrate having activeelements such as thin-film transistors in a stable and high qualitysemiconductor film (silicon film) formed only at desired position on aninsulating substrate. A second object of the invention is to provide aprocess of fabricating the display device, enabling a stable and highquality silicon film to be formed only at desired position on theinsulating substrate. A third object of the invention is to provide anapparatus for implementing the process of fabricating the displaydevice.

To attain the fist object, the insulating substrate (the active matrixsubstrate) of the display device according to the invention comprises amultitude of data lines juxtaposed so as to be extended in a directionon the top surface of the insulating substrate, and a multitude ofscanning lines juxtaposed so as to be extended in another directioncrossing the direction. There are also provided pixel circuits havingactive elements (also referred to as thin-film transistors) such asthin-film transistors, disposed in the vicinity of cross-over points ofthe data lines and the scanning lines. The thin-film transistors aremade of a band-like polycrystalline silicon film having crystallinitydescribed and disposed in a matrix form in a display region. Therespective pixels are made up of pixel circuits having pixel electrodesdriven by the active elements, respectively.

A driving circuit (hereinafter referred to as driver circuit) is dividedand formed at a plurality of spots on at least one side of theinsulating substrate. The active layer (active region) of the thin-filmtransistor making up the driver circuit is obtained by reformationimplemented by scanning the continuous-wave laser light, condensed intoa linear form or a rectangle form extremely longer in the longitudinaldirection than in the transverse direction, along a given directioncrossing the longitudinal direction. This is made up of a poly siliconfilm containing crystal grains having no grain boundaries crossing thedirection of current flow, that is, a band-like polycrystalline siliconfilm.

To attain the second object, the process of fabricating the displaydevice made up of a thin-film transistor substrate comprises the stepsof: taking out continuous-wave laser light at timing required by use ofan electro-optical modulator (hereinafter referred to also EOmodulator); forming the continuous-wave laser light into linear orrectangular form as described above; irradiating the laser light thusformed only to necessary portions including the thin-film transistorpart making up the driver circuit disposed on the outside of the displayregion, and periphery thereof out of amorphous silicon film andamorphous silicon film composed of fine crystal grains, formed on theentire top surface of the insulating substrate such as glass and soforth.

The thin-film transistor substrate with the top surface thereof facingupward is mounted on the stage making relative movement in relation tothe laser light, and the above-described necessary portions of thethin-film transistor substrate are irradiated and scanned by the laserlight, thereby implementing reformation. Such scanning is executed suchthat a pulse signal generated by the linear scale and so forth fordetecting the position of the stage following movement of the stage iscounted, and at a time when a position where the thin-film transistor isto be formed is reached, irradiation of the laser light is started.Further, the pulse signal is counted, and at a time when a region wherethe laser light is to be irradiated is passed, irradiation of the laserlight is stopped. Such operation is repeated while the stage is kept inconstant movement.

With the invention, while the stage is kept in continuous movement, onlynecessary pats can be irradiated with the laser light by turning thecontinuous-wave laser light ON/OFF, and parts where the laserirradiation is not required will not be irradiated, so that occurrenceof melting or aggregation of the silicon film can be prevented. Also, itis possible to prevent thermal damage to a glass substrate etc. as thethin-film transistor substrate. Further, since the start and stoppage ofthe laser light irradiation can be controlled on the basis of theposition of the stage, high precision irradiation start and stop isensured even there occurs variation in the moving speed of the stage.

In Patent Document 2, there has been disclosed a configuration wherein alaser pulse is emitted when a laser irradiation position is opposed to alaser irradiation position as a technology to irradiate laser lightaccurately. In this technology, no consideration is given to the controladopted by the present invention, that is, while keeping the stage inmovement, irradiation of the continuous-wave laser light is started at aspecified position and after irradiation for a predetermined time(predetermined distance), irradiation is stopped.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, objects and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawing wherein:

FIG. 1 is a block diagram for schematically illustrating an embodimentof an apparatus of fabricating a display device according to theinvention for carrying out an embodiment of a process of fabricating thedisplay device according to the invention;

FIG. 2 is a perspective view of the EO modulator 10 in FIG. 1 forexplaining the function thereof;

FIG. 3 is another perspective view of the EO modulator 10 in FIG. 1 forexplaining the function thereof;

FIG. 4 is a graph showing a relationship between applied voltage andtransmittance in the EO modulator;

FIG. 5 is a graph showing a relationship among laser input, appliedvoltage, and laser output in the EO modulator;

FIG. 6 is a plan view for illustrating the glass substrate as the objectfor a laser annealing method, which is an embodiment of a process offabricating the display device according to the invention, and anenlarged view of the principal part thereof is also shown in the figure;

FIG. 7 is a time chart for illustrating the embodiment of the process offabricating the display device, according to the invention, showingtiming of shifting the stage 2 and irradiating the laser light,respectively;

FIG. 8 is a plan view showing crystal morphology prior to the laserannealing according to the embodiment of the process of fabricating thedisplay device according to the invention;

FIG. 9 is a plan view showing crystal morphology after the laserannealing;

FIG. 10 is a plan view of the glass substrate 1, showing a relationshipin position between regions where the laser annealing is applied andactive regions of the driver circuit;

FIG. 11 is a plan view of a substrate, showing a configuration of thethin-film transistors of the driver part formed by the laser annealingaccording to the invention;

FIG. 12 is a schematic representation for illustrating electronicequipment with the display device of the invention mounted therein;

FIG. 13 is a time chart showing timing of shifting a stage andirradiating laser light, respectively, with reference to a laserannealing method, which is said embodiment of the process of fabricatingthe display device according to the invention;

FIG. 14 is a schematic representation for illustrating anotherembodiment of an apparatus, that is, a laser annealing apparatus forfabricating the display device according to the invention;

FIG. 15 is a schematic representation for illustrating the opticalsystem in FIG. 14;

FIG. 16 is a perspective view for illustrating a condensed state of thelaser light, suitable for the laser annealing according to theinvention;

FIG. 17 is a perspective view for illustrating a laser irradiationregion at the time of the laser annealing according to the invention;

FIG. 18 is a plan view of an insulating substrate for illustratinganother embodiment of a process of fabricating the display device,according to the invention;

FIG. 19 is a schematic representation for illustrating a relationshipbetween a stage position according to another embodiment of theinvention and laser output;

FIG. 20 is a sectional view showing the sectional shape of a thin-filmtransistor substrate to which a laser annealing method according to thepresent embodiment is applied;

FIG. 21 is a sectional view showing the sectional shape of a thin-filmtransistor substrate to which the laser annealing method described withreference to FIG. 19A is applied;

FIG. 22 is a flowchart for illustrating the steps of fabricating adisplay device, to which the process of fabrication according to theinvention is applied;

FIG. 23 is a flowchart for illustrating the step of annealing accordingto the invention;

FIG. 24 is a sectional view of the principal part of a liquid crystaldisplay panel of a liquid crystal display device which is an example ofan embodiment of a display device according to the invention forillustrating an example of configuration thereof;

FIG. 25 is a sectional view of the principal part of a liquid crystaldisplay panel of a liquid crystal display device which is an example ofan embodiment of a display device according to the invention forillustrating another example of configuration thereof;

FIG. 26 is a sectional view for illustrating a schematic configurationof a liquid crystal display device using the liquid crystal displaypanel described with reference to FIGS. 24, and 25;

FIG. 27 is a sectional view of the principal part of a display panelmaking up an organic electro-luminescent display panel, another exampleof the display device according to the invention, for illustrating aschematic configuration thereof;

FIG. 28 is a plan view showing a state of annealing region at a firstscanning according to the invention;

FIG. 29 is a plan view showing a state of annealing region at a secondscanning according to the invention;

FIG. 30 is a plan view showing a state of annealing region uponcompletion of scanning according to the invention;

FIG. 31 is a plan view showing regions where transistor can be formedupon completion of annealing according to the invention;

FIG. 32 is a plan view showing a state of annealing region uponcompletion of a first scanning according to another embodiment of theinvention;

FIG. 33 is a plan view showing a state of annealing region uponcompletion of a second scanning according to another embodiment of theinvention;

FIG. 34 is a plan view showing a state of annealing region uponcompletion of annealing according to another embodiment of theinvention; and

FIG. 35 is a schematic representation showing a relative position amongpixel part, peripheral circuit part, and circuit formed in peripheralpart of a panel after laser annealing according to the invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention are described in detail hereinafter withreference to the accompanying drawings.

FIG. 1 is a block diagram for schematically illustrating an embodimentof an apparatus of fabricating a display device according to theinvention for carrying out an embodiment of a process of fabricating thedisplay device according to the invention. In this case, for aninsulating substrate to serve as a thin-film transistor substrate, aglass substrate is used. A glass substrate 1 is movable in one direction(X) and in another direction (Y) crossing the one direction (X) at rightangles, and is placed on a XYθ stage 2 (hereinafter referred to merelyas stage) capable of adjusting both the directions (θ). The stage 2fixedly attached to a platen (not shown) having a vibration isolationmechanism is provided with linear scales (also referred to as linearencoders) 3, 4, for detecting coordinates in the X direction and the Ydirection, respectively.

A laser light irradiation system (an annealing optical system) forperforming reformation of a silicon film comprises a laser oscillator 6for oscillating continuous-wave laser light 18, a shutter 7 forprevention of inadvertent irradiation of the continuous-wave laser light18, a beam expander 8 for expanding the beam diameter of thecontinuous-wave laser light 18, a continuously variable transmittancefilter 9 for adjusting output (energy) of the continuous-wave laserlight 18, an EO (electro-optical) modulator 10 for turning thecontinuous-wave laser light 18 ON/OFF and modulating the laser light 18time-wise as necessary, a power source (driver) 21 of the EO modulator10, a beam forming optics 11 for compressing the continuous-wave laserlight 18 in one direction to be converted into linear beams, anelectromotive rectangular slit 12 for cutting out only a necessaryportion of the continuous-wave laser light 18 converted into the linearbeams, an objective lens 13 for projecting the continuous-wave laserlight 18 passing through the electromotive rectangular slit 12 on theglass substrate 1, a slit reference light source 14 for checkingirradiation position and shape of the continuous-wave laser light 18, anoverhead illuminating light source 15 for shining the surface of theglass substrate 1, and a CCD camera 16 for observation of a glasssubstrate face or detection of alignment marks at the time of alignmentas necessary.

The laser light irradiation system further comprises a controller 22 forperforming opening/closing of the shutter 7, adjustment of transmittanceof the continuously variable transmittance filter 9, control of thepower source (driver) 21 of the EO modulator 10, control of theelectromotive rectangular slits 12, control of the stage 2, processingof respective signals from the linear scales 3, 4, processing of imagesdetected by the CCD camera 16, and so forth. In FIG. 1, as forelectrical connection, there is shown relationship only among the linearscales (linear encoders) 3, 4, the controller 22, the EO modulator 10,and the power source (driver) 21.

For the laser oscillator 6, use is made of one for generating foroscillating continuous oscillation laser light of ultraviolet or visiblelight wavelength, and in particular, one for generating the secondharmonics of LD (laser diode) pumped YVO₄ continuous wave laser isoptimum from the viewpoint of magnitude of output, stability, and soforth. However, the invention is not limited thereto, use may be made ofharmonics and so forth of argon laser and YAG laser. The shutter 7 isinstalled to prevent inadvertent irradiation of the continuous-wavelaser light 18 in the course of transit of the glass substrate 1,positioning thereof, and so forth, and is not intended for use to turnthe continuous-wave laser light 18 ON/OFF at the time of laserannealing. The beam expander 8 is intended to expand the beam diameterin order to prevent damage from occurring to crystals, in particular, ofPockels cell, and so forth, constituting the EO modulator 10 however, inthe case of using Pockels cell capable of withstanding high energydensity, use of the beam expander 8 may be unnecessary.

The continuous-wave laser light 18 oscillated by the laser oscillator 6passes through the shutter 7 in open state, and is expanded in beamdiameter by the beam expander 8 to subsequently fall on the EO modulator10. In this stage, the beam diameter is expanded by the beam expander 8to a size close to the effective diameter of the EO modulator 10 takingpower resistance of the EO modulator 10 into account. In the case wherethe beam diameter of the continuous-wave laser light 18 oscillated bythe laser oscillator 6 is approximately 2 mm, and the EO modulator 10with the effective diameter of 15 mm is used, a suitable ratio ofexpansion by the beam expander 8 is from about 3 to 5 times. The laserlight 18 with the beam diameter expanded by the beam expander 8 falls onthe EO modulator 10.

FIG. 2 is a perspective view of the EO modulator 10 in FIG. 1 forexplaining the function thereof. FIG. 3 is another perspective view ofthe EO modulator 10 in FIG. 1 for explaining the function thereof. Asshown in FIGS. 2 and 3, the EO modulator 10 in this case comprises aPockels cell 61 (hereinafter also referred to as a crystal) combinedwith a polarized beam splitter 62. If the laser light 18 is a linearlypolarized light, it is set such that by applying voltage V1 (normallyvoltage 0V) to the crystal 61 via a power source (not shown) of the EOmodulator 10, as shown in FIG. 2, a polarization direction of the laserlight 18 passing through the crystal 61 is not rotated to be maintainedas it is, and falls as S polarized light on the polarized beam splitter62 to be thereby deflected by 90 degrees. That is, in this state, sincethe laser light 18 is sent out after deflection by 90 degrees, the laserlight 18 does not fall on the rest of the laser light irradiationsystem, and is in OFF state on top of the glass substrate 1.

Further, by applying voltage V2 capable of rotating the direction ofpolarization of the laser light 18 passing through the crystal 61 by 90degrees as shown in FIG. 3, the direction of polarization of the laserlight 18 passing through the crystal 61 is rotated by 90 degrees andfalls as P polarized light on the polarized beam splitter 62, whereuponthe laser light 18 passes through the polarized beam splitter 62, andtravels in a straight line. That is, in this state, since the laserlight 18 travels in the straight line, and falls on the rest of thelaser light irradiation system, the laser light 18 is in ON state on topof the glass substrate 1.

FIG. 4 is a graph showing a relationship between applied voltage andtransmittance in the EO modulator. As is evident from the relationshipbetween voltage applied to the crystal 61 and transmittance of the laserlight 18 passing through the EO modulator 10, shown in FIG. 4, thetransmittance of the laser light 18 passing through the EO modulator 10can be set suitably between T1 (normally 0) and T2 (herein, the maximumtransmittance, that is, 1) by varying the voltage applied to the crystal61 between V1 (normally, 0V) and V2. That is, the transmittance of thelaser light 18 passing through the EO modulator 10 can be set suitablybetween 0 and 1. In this case, however, it is presumed that reflectionand absorption do not take place on the surface of the crystal 61 andthe polarized beam splitter 62, respectively.

FIG. 5 is a graph showing a relationship among laser input, appliedvoltage, and laser output in the EO modulator. On the basis ofdescription given with reference to FIGS. 3 and 4, by varying voltageapplied to the crystal 61 to V1, V2, V3, and V1 in stages while output(input to the EO modulator 10) of the laser light 18 falling on the EOmodulator 10 is kept constant, pulse output of P2, P3 in stages as laseroutput from the EO modulator 10 can be obtained as shown in FIG. 5.Herein, the output P2 is found as the product of the input to the EOmodulator 10, P0, and the transmittance T2 when the voltage V2 isapplied and the output P3 is found as the product of the input P0, andthe transmittance T3 when the voltage V3 is applied. It is evident thatthe laser light 18 passing through the EO modulator 10 can besuccessively varied by successively varying the voltage applied to thecrystal 61, so that the laser light 18 pulsing and having variation withtime can be obtained.

Now, it has been described hereinabove that the Pockels cell 61 incombination with the polarized beam splitter 62, is used as the EOmodulator 10, however, in place of the polarized beam splitter 62,various sheet polarizers can be used. In description given hereinafter,the Pockels cell 61 in combination with the polarized beam splitter 62(or sheet polarizer) will be referred to as the EO modulator 10.

Further, besides the EO modulator 10, an AO (acousto-optical) modulatormay be used. However, because the AO modulator generally has a lowerdriving frequency as compared with the EO modulator, there is apossibility of the AO modulator being unsuitable in the case where fastrising and falling are required or pulse light with a small pulse widthis cut out. Thus, with the use of a modulator such as the EO modulator10 or the AO modulator, in a state where the continuous-wave laser lightis constantly sent out from the laser oscillator 6, it is possible tostart irradiation to an optional spot of irradiation start on a part asthe object of irradiation, and to complete irradiation to an optionalspot of irradiation completion thereof.

The laser light 18 turned into ON state by the EO modulator 10 is formedinto a beam in a desired shape by the beam forming optics 11. Since anoutput beam from a gas laser oscillator and a solid-state laseroscillator, respectively, normally has Gaussian energy distributioncircular in shape, the same cannot be used as it is for the laserannealing according to the invention. If output from the oscillator issufficiently large, by sufficiently expanding the beam diameter of thelaser light, and cutting out a necessary shape from a relatively uniformportion at the center thereof, a suitable shape with substantiallyuniform energy distribution can be obtained, however, this result indiscarding the peripheral part of the laser light, so that most ofenergy will be wasted.

In order to convert the Gaussian distribution into a uniformdistribution for overcoming the shortcoming, a beam homogenizer is usedas necessary. Otherwise, by condensing the laser light 18 only in onedirection with a cylindrical lens, a linear beam can be obtained on thesurface of the electromotive rectangular slit 12. In FIG. 1, thecylindrical lens only is shown as the beam forming optics 11.

Now, reverting to FIG. 1, operation of the fabrication apparatusaccording to the invention is described hereinafter. Unnecessaryperipheral portions of the laser light 18 condensed into a linear formby the cylindrical lens 11 are cut off by the electromotive rectangularslit 12 to be thereby formed into a rectangular form as desired (deemedas linear in macroscopic terms), which is then projected on the glasssubstrate 1 by the objective lens 13 after demagnification. In the caseof condensing the laser light into a linear form by the cylindrical lens11, energy distribution in the longitudinal direction remains asGaussian while energy distribution on both edges is lower.

Accordingly, low energy density portions thereof, normally unsuitablefor annealing, are cut off by the electromotive rectangular slit 12. Asa result, by scanning the laser light condensed in a linear form in thedirection of the width thereof, an annealing process can besatisfactorily applied an entire scanned part. Assuming that amagnification of the objective lens 13 is M, an image of theelectromotive rectangular slit 12, or the laser light 18 passing throughthe face of the electromotive rectangular slit 12 is projected in sizecorresponding to the reciprocal of the magnification, that is, 1/M.

Upon irradiation of the glass substrate 1 with the laser light 18, thelaser light 18 is irradiated to a desired spot at a pulse while thestage 2 is being shifted in an X-Y plane, but if defocusing occurs dueto asperities, undulation, and so forth, present on the surface of theglass substrate 1, there occurs variation in power density of the laserlight 18 as condensed and deterioration in irradiation shape, so that anintended object cannot be attained. Accordingly, by detecting a focusingposition with an automatic focusing optical system (not shown) to enableirradiation to be directed to the focusing position all the time,control is implemented such that the focusing position (projectionposition of the face of the electromotive rectangular slit 12) is inagreement with the glass substrate 1 all the time by driving the stage 2in the Z-direction (height direction) or by driving the optical systemin the Z-direction (height direction) in case the laser light 18 is offthe focusing position. The surface of the glass substrate 1 irradiatedwith the laser light 18 can be illuminated by illuminating light fromthe overhead illuminating light source 15.

The surface of the glass substrate 1 is photographed with the CCD camera16 so as to be observed with a monitor (not shown). When observing thesurface of the glass substrate 1 during laser irradiation, a laser cutfilter is inserted before the CCD camera 16 to thereby prevent halationfrom occurring to the CCD camera 16 caused by the laser light 18reflected from the surface of the glass substrate 1, resulting infailure to observe, and to prevent occurrence of damage to the CCDcamera 16 in the extreme case.

Alignment of the glass substrate 1 placed on the stage 2 can be madealong three axes of X, Y, θ by driving the stage 2 after taking picturesof the alignment mark provided on the glass substrate 1, corners of theglass substrate 1, or specific patterns at a plurality of spots, withuse of the objective lens 13 and the CCD camera 16, and calculatingcoordinates of respective positions thereof by performing imageprocessing such as binarization processing of those pictures, andpattern matching, etc. with the controller 22, respectively, asnecessary.

In FIG. 1, only one piece of the objective lens 13 is shown, however, byfitting an electromotive revolver with a plurality of objective lenses,and changing over those objective lenses as appropriate, proper use canbe made of an optimal one of those objective lenses, corresponding tothe content of processing. More specifically, use can be made of anobjective lens optimal to the alignment at the time of placing the glasssubstrate 1 on the stage 2, fine alignment to be executed if needed,laser annealing processing, observation after the processing, formationof an alignment mark which will be described later, and so forth,respectively. Alignment can be provided by installing an optical system(lens, camera, and illumination device) for exclusive use, however, useof the optical system for the laser annealing in common with an opticalsystem for alignment enables detection along an identical optical axis,thereby enhancing precision of detection.

Now, there will be described hereinafter an embodiment of a process offabricating a display device, that is, a process of laser annealing,according to the invention, using the above-described fabricationapparatus according to the invention. Herein, a glass substrate 1 as anobject for annealing is obtained by forming an amorphous silicon film (anon-crystalline silicon film) 40 to 150 nm thick on the top surface of aglass substrate on the order of 0,3 to 1.0 mm thick through theintermediary of an insulator thin film, and by scanning across theamorphous silicon film with excimer laser light before crystallizing thesame into a polysilicon film (polycrystalline silicon film). This ishereinafter referred to merely as the glass substrate 1 at times. Inthis case, the insulator thin film is a SiO₂, or SiN film, 50 to 200 nmthick, or a composite film thereof.

FIG. 6 is a plan view for illustrating the glass substrate as the objectfor a laser annealing method, which is an embodiment of a process offabricating the display device according to the invention, and anenlarged view of the principal part thereof is also shown in the figure.The glass substrate 1 with the polysilicon film formed thereon afterexcimer laser annealing is placed on the stage 2 in FIG. 1. As shown inFIG. 6, the glass substrate 1 comprises a display region 101, which is apixel part, and driver circuit regions 102, 102′, and alignment marks103, 103′ are formed at least two spots on an outer edge thereof. Thesealignment marks 103, 103′ may be formed by photo-etching techniques,however, use of a photo resist step for this purpose only will result inmuch wastage.

Accordingly, the laser light 18 for use in laser annealing is formed inthe shape of, for example, a rectangle longer in the longitudinaldirection and a rectangle longer in the transverse direction,respectively, in sequence by rotation of the cylindrical lens 11, and byuse of the electromotive rectangular slit 12 to thereby remove portionsof the polycrystalline silicon film, thus forming cross marks, which areto serve as the alignment marks 103, 103′, respectively. Otherwise,dot-like alignment marks may be formed by ink-jet means and so forth. Inthese cases, pre-alignment needs to be provided in corners and so forthof the glass substrate 1.

While respective positions of the alignment marks 103, 103′ aredetected, and the positions are corrected in terms of X, Y, θ (X-axis,Y-axis, θ-axis), and subsequently, the optical system is shifted in thedirection indicated by the arrow in FIG. 6 or the stage 2 is shifted inthe direction opposite thereto in accordance with design coordinates soas to be relatively scanned, the laser light 18 turned into ON state bythe EO modulator 10 is condensed by the objective lens 13 and isirradiated. Regions irradiated with the laser light 18 are, for example,driver circuit parts 102, 102′, for driving the respective pixels, in astricter sense, thin-film transistor forming regions of a driver part(parts indicated by 104, 105, 106, 107, 108, 109, and 110 in theenlarged view in FIG. 6, hereinafter referred to also as annealingregions). While the glass substrate 1 is reciprocatively shiftedrelatively a plurality of times as necessary, the laser light 18 issequentially irradiated. Depending on a configuration of the fabricationapparatus, relative scanning may be executed by shifting the opticalsystem.

FIG. 16 is a perspective view for illustrating a condensed state of thelaser light, suitable for the laser annealing according to theinvention. Respective sizes of the annealing regions 104 through 110are, for example, 4 mm×100 μm, and these rectangular regions are set atpitches of 250 μm. Meanwhile, the size of a laser beam irradiated is 500μm×10 μm. That is, as shown in FIG. 16, the laser beam is formed in theshape of a rectangle (band) 500 μm in the longitudinal direction and 10μm in the transverse direction.

Suitable energy density of the laser light irradiated at this time is ina range of about 100×10³ W/cm² to 500×10³ W/cm², however, the optimumvalue varies depending on scanning speed of the laser light, thicknessof the silicon film, whether the silicon film is amorphous orpolycrystalline, and so forth. In the case of using a laser oscillatorwith output at 10 W, since the width of a region that can be annealed byone scanning is 500 μm, it is necessary to execute one way scanning 8times or reciprocative scanning 4 times in order to implement annealingof a required width (4 mm). The width of the region that can be annealedis dependent on the output of the laser oscillator 6, so that if theoutput of the laser oscillator 6 is sufficiently large, it is possibleto irradiate a larger region, thereby reducing scanning times. Or it isalso possible to render an irradiating laser beam in a shape smaller incondensed light width or greater in the longitudinal direction.

FIG. 17 is a perspective view for illustrating a laser irradiationregion at the time of the laser annealing according to the invention.While relatively shifting the glass substrate 1 at a speed of 500 mm/s,the glass substrate 1 is irradiated up to a length 100 μm only atpitches of 250 μm in a manner shown in FIG. 17. That is, irradiationwith the laser light is started at an irradiation start position, andthe stage 2 is relatively shifted 100 μm while maintaining theirradiation with the laser light, stopping the irradiation with thelaser light at an irradiation completion position.

Subsequently, at a spot where the stage 2 is shifted 250 μm, irradiationstart and irradiation termination are again executed, which is repeatedas many times as necessary. By so doing, there is formed an annealingregion approximately 500 μm×100 μm (in a stricter sense, an annealingregion 500 μm×110 μm if the width of the irradiating laser light istaken into account) at the pitches of 250 μm, and as explained in detaillater, grain growth occurs in the direction of scanning with the laserlight.

FIG. 7 is a time chart for illustrating the embodiment of the process offabricating the display device, according to the invention, showingtiming of shifting the stage 2 and irradiating the laser light,respectively. The controller 22 is provided with counters C1 through C4(not shown). Herein, there is described a procedure for irradiating thelaser light 18 while relatively scanning the glass substrate 1 afterturning the same ON/OFF with the EO modulator 10.

By scanning in the X-direction as indicated by the arrow in FIG. 6, thelaser light 18 is irradiated to 1024 spots for a distance of 100 μm onlyat the pitches of 250 μm. Every time the stage 2 is shifted for apredetermined distance in the X-direction, the linear scale (the linearencoder) 3 securely attached to the x-axis of the stage 2 generates onepulse of pulse signal. If the signal generated is a sinusoidal wave, thesame may be converted into a rectangular wave for use. By counting thepulse signal, a position of the stage 2 can be detected. In the case ofthe linear scale 3 with high precision, one pulse of the pulse signal isgenerated by the linear scale 3, for example, for every 0.1 μm in shiftamount. In case a pulse interval is large, the pulse interval can berendered into smaller intervals through electrical division.

The stage 2 requires a given distance (an acceleration region) to reacha given speed from a stop condition. Assuming that a stage speed at thetime of laser irradiation is 500 mm/s, the acceleration region on theorder of 50 mm is necessary, and positioning of the stage 2 is made at aposition (at Xs in FIG. 7) not less than 50 mm, as the accelerationregion, for example, 60 mm, to the left from the irradiation startposition (the left edge of the annealing region 104 in FIG. 6) beforestopping.

At this point in time, a counter circuit C1 (the counter C1) forcounting the pulse signal from the linear scale 3 according to a commandof the controller 22 starts counting after clearing counter numbers onceand concurrently, starts driving the stage 2. The counter circuit C1counts the pulse signal generated following a shift of the stage 2, andsends out a gate-ON signal (gate ON) at a point in time when the stage 2has reached the first irradiation start position X1, that is, pulsenumbers n1 (600000 pulses) correspond to a shift of 60 mm are counted.The gate-ON signal opens a gate to the power source 21 of the EOmodulator 10, enabling the signal to be transmitted thereto. By thispoint in time, the stage speed has completed acceleration, havingreached the given speed.

Upon receiving the gate-ON signal, a counter circuit C3 (the counter C3)sends out an ON signal (EOM-ON) for the power source 21 of the EOmodulator, and concurrently, starts counting after clearing countnumbers, thereafter sending out the ON signal to the power source 21 ofthe EO modulator every time when pulse numbers n3 (2500 pulses)corresponding to a pitch of irradiation are counted. Meanwhile, a timerT1 (timer 1) (not shown) incorporated in the controller 22.

Meanwhile, upon receiving the ON signal to the power source 21 of the EOmodulator, a counter circuit C4 (the counter C4) starts counting whileclearing count numbers, and sends out an OFF signal (EOM-OFF) to thepower source 21 of the EO modulator at a point in time when pulsenumbers n4 (1000 pulses) corresponding to the length 100 μm of theannealing region are counted. This operation is repeated every time whenthe counter circuit C3 sends out the ON signal for the power source 21of the EO modulator.

During a time period from receipt of the ON signal for the power source21 of the EO modulator until receipt of the OFF signal for the powersource 21 of the EO modulator (time required for the stage 2 to passover a distance of 100 μm at the stage speed of 500 mm/s), the powersource 21 of the EO modulator applies a voltage for causing thepolarization direction of the laser light 18 to be rotated by 90 degreesto the Pockels cell 61. As a result, the laser light 18 passes thoughthe EO modulator 10 to be irradiated to the substrate 1 only for timecorresponding to time when the voltage is applied to the Pockels cell61.

Meanwhile, upon receiving the gate-ON signal from the counter circuitC1, a counter circuit C2 (the counter C2) clears count numbers, countsthe OFF signals for the power source 21 of the EO modulator, send out bythe counter circuit C4, and closes the gate at a point in time whenpulse numbers n2 (1024 pulses) corresponding to the number of theannealing regions are counted. As a result, the power source 21 of theEO modulator no longer receives the ON signal for the power source 21 ofthe EO modulator, and the OFF signals for the power source 21 of the EOmodulator, so that the power source 21 of the EO modulator stops itsoperation.

In accordance with the procedure described above, the first laserannealing for the driver circuit region 102 shown in FIG. 6 iscompleted, however, since the driver circuit region, in practice, isseveral mm in width, the glass substrate 1 in whole cannot be annealedwith one scanning. Accordingly, after shifting the glass substrate 1 inthe Y-direction by a given pitch (with the present embodiment, 500 μm),the above-described procedure is repeated. By so doing, in a state wherethe stage 2 is continuously shifted, the laser light 18 can beirradiated with high precision without being affected in any way byvariation in the stage speed. However, when scanning is repeated, thereare cases where annealed portions are overlapped in parallel with ascanning direction or portions not irradiated with the laser light 18occur. Because grain growth is disturbed in those portions, it isdesirable to consider a layout design such that no transistor is formedin portions where scanned parts are overlapped with each other.

Now, behavior of a polycrystalline silicon thin film upon irradiationthereof with the laser light 18 is described hereinafter.

As previously described, with the present embodiment, the glasssubstrate 1 obtained by forming the polycrystalline silicon thin film onthe top surface of the glass substrate by the excimer laser annealing(that is, reformation) is used as the object for annealing.

FIG. 8 is a plan view showing crystal morphology prior to the laserannealing according to the embodiment of the process of fabricating thedisplay device according to the invention, FIG. 9 is a plan view showingcrystal morphology after the laser annealing, and FIG. 10 is a plan viewof the glass substrate 1, showing a relationship in position betweenregions where the laser annealing is applied and active regions of thedriver circuit. The polycrystalline silicon thin film obtained by theexcimer laser annealing is an aggregate of fine crystal grains 120, 121,not more than 1 μm (several 100 nm) in grain size as shown in FIG. 8.Upon irradiation of regions shown in the figure with the laser light,the fine crystal grains 120 outside of laser irradiation regions areleft intact, however, fine crystal grains (for example, the crystalgrains 121) within the laser irradiation regions melt. Thereafter, withpassage of each of the laser irradiation regions, the crystal grains 121are rapidly solidified and recrystallized.

Hereupon, melted silicon uses crystal grains remaining on the peripheryof melted parts as seed crystals, and crystals following the crystalorientation of the seed crystals undergo growth in the scanningdirection of the laser light in accordance with temperature gradient. Atthis point in time, since a growth rate of crystal grains variesdepending on the crystal orientation, only the crystal grains having thecrystal orientation with the fastest growth rate eventually continuecrystal growth.

More specifically, as shown in FIG. 9, growth of a crystal grain 122having the crystal orientation with a slow growth rate is suppressed bygrowth of crystal grains 124, 126, surrounding the crystal grain 122,having the crystal orientation with a faster growth rate, respectively,so that crystal growth thereof stops. Further, a crystal grain 123 andthe crystal grain 124, having the crystal orientation with anintermediate growth rate, respectively, continue growth, however, growththereof is suppressed by growth of crystal grains 125, 126, having thecrystal orientation with a still faster growth rate, respectively, sothat crystal growth thereof stops before long. Eventually only thecrystal grains 125, 126, and a crystal grain 127, having the crystalorientation with the fastest growth rate, respectively, continue growth.These crystal grains 125, 126, 127, continuing crystal growth until thelast are individual crystal grains in a strict sense, but have nearlythe same crystal orientation, so that a melted and recrystallized partcan be effectively regarded as a single crystal.

By irradiating the laser light to the polycrystalline silicon thin filmas described hereinbefore, only portions irradiated with the laser lightare annealed in the shape of islands, and only crystal grains having aspecific crystal orientation undergo growth, thereby forming regions ofthe crystal grains 125, 126, 127, having properties substantiallysimilar to those of a single crystal, although in polycrystalline statein a strict sense. These regions can be effectively regarded as a singlecrystal particularly in the direction not crossing the grain boundaries,that is, in the scanning direction of the laser light. With the presentinvention, the silicon film crystallized in this way is called aband-like polycrystalline silicon film.

By repeating the procedure described while relatively scanning the galssubstrate 1, and by sequentially irradiating portions requiringannealing with the laser light, all the thin-film transistor (thin-filmtransistor of the driver part) forming regions of the driver circuit canbe converted into regions of the band-like polycrystalline silicon filmhaving properties similar to those of the single crystal. Further,because in the regions having properties similar to those of the singlecrystal, the growth of the crystal grains has taken place in a givendirection as shown in FIG. 9, it is possible to cause a direction ofcurrent flow to coincide with a direction of grain growth when formingthe transistors, thereby preventing current from flowing in such adirection as to cross grain boundaries.

FIG. 11 is a plan view of a substrate, showing a configuration of thethin-film transistors of the driver part formed by the laser annealingaccording to the invention. That is, alignment can be made such thatportions of a laser irradiation region 301, made up of the crystalgrains having a high growth rate, respectively, correspond to activelayers (or active regions) 302, 303 of the thin film transistors of thedriver circuit, respectively, as shown in FIG. 10. After impuritiesimplantation process and photo-etching process, regions other than theactive regions 302, 303 are removed, and there are formed a gateelectrode 305 through the intermediary of a gate insulating film, asource electrode 306 and a drain electrode 307, having ohmic connection,thereby completing a thin-film transistor. In this case, grainboundaries 304, 304′ exist in the active region 303, but since currentflows between the source electrode 306 and the drain electrode 307, thecurrent does not flow across the grain boundaries 304, 304′, so thatmobility equivalent to that in the case where the active region iseffectively made of a single crystal can be obtained.

As described above, in the part melted and reacrystallized by the laserannealing according to the invention, by causing the direction ofcurrent flow to coincide with the direction of crystal grain boundariesso as not to allow current to flow in such a direction as to cross thegrain boundaries, mobility can be improved more than twice as comparedwith a case where annealing with the excimer laser is simply applied,more specifically, to more than 350 cm²/Vs. Such a mobility value issufficient to constitute a driver circuit capable of driving liquidcrystals at a high speed.

Meanwhile, transistors for switching the pixel part (thin-filmtransistors of the pixel part) are formed in the region 101 ofpolycrystalline silicon film, where annealing with the excimer laser issimply applied. With a polycrystalline film obtained by the annealingwith the excimer laser, crystal grains are fine, and the crystalorientations thereof are at random, so that mobility is small ascompared with the case of the crystal grains obtained by the excimerlaser annealing according to the invention, however, such mobility isgood enough for the thin-film transistors for switching the pixel part,that is, the thin-film transistors of the pixel part.

In some cases, even an amorphous silicon film can be sufficient for usein the thin-film transistors of the pixel part. In such a case, anamorphous silicon thin film is formed on top of the glass substrate 1,and it is sufficient that the excimer laser annealing according to theinvention is not applied thereto while the excimer laser annealingaccording to the invention is applied to the driver circuit parts only.Silicon initially melted by irradiation with the laser light 18 isturned into fine polycrystalline state in the course of solidificationthereof, and crystal grains formed in this stage serve as seed grains,whereupon growth of crystal grains having various crystal orientationstakes place, however, as with the case where the silicon film inpolycrystalline state, formed by the excimer laser annealing, isirradiated with the laser light 18, only crystal grains having crystalorientations with the fastest growth rate eventually continue crystalgrowth, thereby forming a polycrystalline silicon thin film regardedeffectively as a single crystal.

After completion of the laser annealing applied to the driver circuitregion 102 shown in FIG. 6, the driver circuit region 102′ needsannealing. In this case, the glass substrate 1 may be rotated by 90degrees or a scanning direction may be altered by 90 degrees. In thelatter case, it is necessary to rotate a beam-forming device (in FIG. 1,the cylindrical lens 11) by 90 degrees and to switch over between thetransverse direction and the longitudinal direction of the rectangularslit. Further, the driver circuit region 102 shown in FIG. 6 is normallya data driver circuit region (referred to as a drain driver whenthin-film transistors are used as the active elements) and the drivercircuit region 102′ shown in FIG. 6 is a scanning driver circuit region(referred to as a gate driver when thin-film transistors are used as theactive elements).

In the case of the glass substrate 1 shown in FIG. 6, if transistorsrequiring fast operation can be put together in either of the drivercircuit regions 102, 103, for example, in the driver circuit region 102,the laser annealing according to the invention may be applied to thedriver circuit region 102 only. In other words, the active layers(active regions) of the transistors formed in the driver circuit region102 are made of polycrystalline silicon containing crystal grains havingno grain boundaries in the direction of current flow, so that fastoperable transistors can be obtained.

On the other hand, since thin-film transistors not requiring so fastoperation are formed in the driver circuit region 102′, the activelayers (active regions) of the transistors are made up of apolycrystalline silicon film composed of fine crystal grains, simplyannealed by the excimer laser. In this case, since it becomesunnecessary to rotate the substrate or the scanning direction and thedirection of the linear beam, and in addition, regions to be annealedcan be reduced, the effect of improvement in throughput is large.

FIG. 18 is a plan view of an insulating substrate for illustratinganother embodiment of a process of fabricating the display device,according to the invention. With the present embodiment, driver circuitregions as objects for the laser annealing are put together on one sideof an insulating substrate (glass substrate). As shown in FIG. 18, if adriver circuit region 602 formed on top of a glass substrate 1 can beput together on one side thereof, outside of a pixel region 601, activelayers (active regions) of all thin-film transistors of a driver partare made up of a polycrystalline silicon film containing crystal grainshaving no grain boundaries in the direction of current flow, so thatfast operable transistors can be obtained. In addition, it becomesunnecessary to rotate the substrate or a scanning direction and thedirection of a linear beam, so that such a configuration is preferablefrom the viewpoint of improvement in throughput. However, a plurality ofalignment marks, for example, alignment marks 603, 603′, shown in thefigure, are evidently required.

Further, with reference to the embodiment previously described, it hasbeen described that the signals from the linear scales (linear encoders)installed in the stage 2 are counted for detecting the position or shiftamount of the stage 2. However, the invention is not limited thereto,and use may be made of output signals from a measuring machine usinglaser light interference, a rotary encoder installed on the axis of amotor driving the stage, and so forth. A process of fabricating athin-film transistor substrate (an active matrix substrate) includingthe above-described procedure for reformation of the band-likepolycrystalline silicon film according to the invention can be summed upin respective flowcharts in FIGS. 22 and 23.

FIG. 22 is a flowchart for illustrating the steps of fabricating adisplay device, to which the process of fabrication according to theinvention is applied. In this case, the steps of fabricating a liquidcrystal display device are described by way of example. FIG. 23 is aflowchart for illustrating the step of annealing according to theinvention. The respective steps are indicated by reference numeralsP-XX. As shown in FIG. 22, an insulating film is formed on top of asubstrate (P-1), an a —Si (amorphous silicon) film is formed (P-2), andexcimer laser annealing is applied (P-3) before applying laser annealingaccording to the invention (P - 4) only to active layer part ofrespective transistors making up a driver circuit, and the peripherythereof. Details of a process of the laser annealing according to theinvention (P-4) are shown in FIG. 23.

In FIG. 23, the substrate (glass substrate) with the excimer laserannealing applied thereto (P-3) is mounted on the stage 2 of afabrication apparatus (laser annealing apparatus) according to theinvention, described with reference to FIG. 1 (P-41), pre-alignment isexecuted in edge faces or corners of the substrate (P-42), and alignmentmarks are formed by laser beam machining (P-43). After execution ofalignment (fine alignment) by detecting the alignment marks (P-44),laser annealing is applied in accordance with design data only to theactive layer part of the respective transistors making up the drivercircuit, and the periphery thereof (P-45). If the alignment marks havealready been formed by other means such as a photo resist process and soforth at the time of mounting the substrate on the laser annealingapparatus, there is no need for the steps of executing the pre-alignment(P-42), and forming the alignment marks (P-43). After repeating thelaser annealing until all intended regions are annealed (P-46), thesubstrate is transported (P-47).

Thereafter, as shown in FIG. 22, in the step pf photo-etching (P-5),only necessary portions of a polycrystalline silicon film are leftintact in the shape of islands on the basis of the alignment marks 103,103′ or coordinates of an origin point as calculated from the alignmentmarks 103, 103′. Subsequently, after a photo-resist process comprisingthe step of gate insulating film formation (P-6), and the step of gateelectrode formation (P-7), there are executed the steps of impuritiesimplantation (P-8), and activation of implanted regions (P-9),respectively. Thereafter, after a further photo-resist processcomprising the steps of interlayer insulator formation (P-10), sourceelectrode and drain electrode formation (P-11), and passivation filmformation (P-12), there are formed the driver circuit and the pixel part101, thereby completing a TFT substrate (LCD (panel) step) (P-13). Thealignment marks 103, 103′ are used for alignment in at lest onephoto-resist process after the laser annealing according to theinvention. Thereafter, alignment marks newly formed by the photo-resistprocess described as above may be used. The thin-film transistors inFIG. 11 are shown merely by way of example, and the invention is notlimited thereto. It is obvious that thin-film transistors can havevarious constructions, and the thin-film transistors of the inventionmay be formed in such a manner as to have constructions withoutdeparting from the spirit and scope of the invention.

Meanwhile, the transistors for switching the pixel part (the thin-filmtransistors of the pixel part) are formed in the region 101 ofpolycrystalline silicon film, where the annealing with the excimer laseris simply applied. That is, after a photo-resist process executed forgate insulating film formation, gate electrode formation, impuritiesimplantation, activation of implanted regions, source electrode anddrain electrode formation, passivation film formation, and so forth, onthe basis of the alignment marks 103, 103′ or coordinates of an originpoint as calculated from the alignment marks 103, 103′, there iscompleted a TFT substrate.

Subsequently, after executing the LCD (panel) step of forming analignment layer on the TFT substrate as completed, overlaying colorfilters on top of the TFT substrate after a rubbing step, and sealing inliquid crystal material, and a module step (P-14) of assembling togetherwith a backlight, there is completed a liquid crystal display device(so-called system on panel) with a high-speed driver circuit formed onthe glass substrate thereof.

With the above-described embodiment of the invention, it has beendescribed that the polycrystalline silicon thin film formed by theexcimer laser annealing, composed of fine crystal grains, is used as theobject for the laser annealing according to the invention. When apolycrystalline silicon thin film is formed directly on the substrate,polycrystalline silicon (Poly-Si) film formation is substituted fornon-crystalline, that is, amorphous silicon (a —Si) film formation inthe flowchart shown in FIG. 22, so that the step of applying the excimerlaser annealing can be omitted, still obtaining the same advantageouseffect as that for the above-described embodiment.

FIG. 12 is a schematic representation for illustrating electronicequipment with the display device of the invention mounted therein. Thedisplay device of the invention can be mounted in a display part of a TVreceiver 401 shown in FIG. 12A, a mobile phone 402 shown in FIG. 12B, ora notebook PC 403 shown in FIG. 12C. Other applications include adisplay of various instruments housed in a dashboard of a car, a displayof a potable game device, a monitor display of a VTR or digital camera,and so on. Further, the display device of the invention can be used as adisplay device using an organic electro-luminescent display panel andother panel type display devices besides the liquid crystal displaydevice using a liquid crystal display panel.

Now, there is described hereinafter another embodiment of a process offabricating the display device according to the invention. FIG. 13 is atime chart showing timing of shifting a stage and irradiating laserlight, respectively, with reference to a laser annealing method, whichis said embodiment of the process of fabricating the display deviceaccording to the invention. There is described an example where as withthe case of the previously-described embodiment, while scanning in theX-direction indicated by the arrow in FIG. 6, laser light is irradiatedto 1024 spots for a distance of 100 μm only at the pitches of 250 μm.The embodiment differs from the previously described embodiment inrespect of a procedure for turning the laser light ON/OFF with an EOmodulator while relatively scanning the substrate.

The linear scale 3 securely attached to the x-axis of the stage 2 inFIG. 1 generates a pulse signal at a given interval so as to correspondto a shift of the stage 2 in the X-direction. If the signal generated isa sinusoidal wave, the same may be converted into a rectangular wave foruse. By counting the pulse signal, a position of the stage 2 can bedetected. In the case of the linear scale 3 with high precision, onepulse of the pulse signal is generated by the linear scale 3, forexample, for every 0.1 μm in shift amount. In case a pulse interval islarge, the pulse interval can be rendered into smaller intervals throughelectrical division.

The stage 2 requires a given distance (an acceleration region) to reacha given speed from a stop condition. Assuming that a stage speed at thetime of laser irradiation is 500 mm/s, the acceleration region on theorder of 50 mm is necessary, and positioning of the stage 2 is made at aposition (at Xs in FIG. 7) not less than 50 mm, as the accelerationregion, for example, 60 mm, to the left from the irradiation startposition (the left edge of the annealing region 104 in FIG. 6) beforestopping.

At this point in time, a counter circuit C1 (the counter C1) forcounting the pulse signal from the linear scale 3 according to a commandof the controller 22 starts counting after clearing counter numbers onceand concurrently, starts driving the stage 2. The counter circuit C1counts the pulse signal generated following a shift of the stage 2, andsends out a gate-ON signal (gate ON) at a point in time when the stage 2has reached the first irradiation start position X1, that is, pulsenumbers n1 (600000 pulses) correspond to a shift of 60 mm are counted.The gate-ON signal opens a gate to the power source 21 of the EOmodulator 10, enabling the signal to be transmitted thereto. By thispoint in time, the stage speed has completed acceleration, havingreached the given speed.

Upon receiving the gate-ON signal (gate ON), a counter circuit C3 (thecounter C3) sends out an ON signal (EOMON) for the power source 21 ofthe EO modulator, and concurrently, starts counting after clearing countnumbers, thereafter sending out the ON signal to the power source 21 ofthe EO modulator every time when pulse numbers n3 (2500 pulses)corresponding to a pitch of irradiation are counted.

Meanwhile, upon receiving the ON signal of the power source 21 of the EOmodulator, a timer T1 (not shown) (timer 1) incorporated in thecontroller 22 starts counting time, and sends out an OFF signal (EOMOFF)to the power source 21 of the EO modulator at a point in time, with theelapse of time (200 μs) required for shifting across an anneal distanceof 100 μm. Otherwise, upon receiving the ON signal of the power source21 of the EO modulator, a pulse signal having a pulse widthcorresponding to time (200 μs) required for shifting across an annealdistance of 100 μm may be generated. This operation is repeated everytime the ON signal of the power source 21 of the EO modulator isreceived.

During a time period from receipt of the ON signal for the power source21 of the EO modulator until receipt of the OFF signal for the powersource 21 of the EO modulator (time required for the stage 2 to passover a distance of 100 μm at the stage speed of 500 mm/s), the powersource 21 of the EO modulator applies a voltage for causing thepolarization direction of the laser light 18 to be rotated by 90 degreesto the Pockels cell 61. As a result, the laser light 18 passes thoughthe EO modulator 10 to be irradiated to the substrate 1 only for timecorresponding to time when the voltage is applied to the Pockels cell61.

In this connection, for use as the power source 21 of the EO modulator,there is available another type capable of applying a voltage waveformcorresponding to a pulse signal waveform by receiving a pulse signalfrom outside. In such a case, a pulse generator may be used in place ofthe timer T1. That is, the ON signal of the power source 21 of the EOmodulator, generated every time the pulse numbers n3 (2500 pulses)corresponding to the pitch of irradiation are counted by the countercircuit C3 is delivered to the pulse generator to thereby generate asignal with a predetermined pulse width, that is, a pulse widthcorresponding to time required for the laser light passing through theannealing region (in the case of the present embodiment, the pulsewidth: 200 μs), and the signal is delivered to the power source 21 ofthe EO modulator. By so doing, as with the above-described embodiment,the laser light can be irradiated to necessary regions on the substrate1.

Meanwhile, upon receiving the gate-ON signal from the counter circuitC1, a counter circuit C2 (the counter C2) clears count numbers, countsthe OFF signals for the power source 21 of the EO modulator, sent out bythe counter circuit C4, or output pulses of the pulse generator, andcloses the gate at a point in time when pulse numbers n2 (1024 pulses)corresponding to the number of the annealing regions are counted. As aresult, the power source 21 of the EO modulator no longer receives theON signal for the power source 21 of the EO modulator, and the OFFsignals for the power source 21 of the EO modulator, so that the powersource 21 of the EO modulator stops its operation.

With the present embodiment, the irradiation start position of the laserlight is controlled by a position of the stage, however, the irradiationcompletion position of the laser light is regulated by time elapsed fromthe start of laser irradiation or a pulse width of the output pulse ofthe pulse generator. Accordingly, if there is variation in the stagespeed, there is a possibility of slight variation of the irradiationcompletion position, corresponding to the variation in the stage speed.When the stage of relatively large mass is being shifted at a highspeed, however, the variation in the stage speed is slight, and aneffect due to the variation in the stage speed is effectively verysmall. In case the stage speed varies on the order of ±1%, there is novariation in the irradiation start position, and variation of theirradiation completion position is to the extent of about of 1 μm, sothat no problem occurs in practice.

In accordance with the procedure described above, the first laserannealing for the driver circuit region 102 shown in FIG. 6 iscompleted, however, since the driver circuit region, in practice, isseveral mm in width, the glass substrate 1 in whole cannot be annealedwith one scanning. Accordingly, after shifting the glass substrate 1 inthe Y-direction by a given pitch (with the present embodiment, 500 μm),the above-described procedure is repeated. By so doing, in a state wherethe stage 2 is continuously shifted, the laser light 18 can beirradiated with high precision without being affected in any way byvariation in the stage speed. However, when scanning is repeated, thereare cases where annealed portions are overlapped in parallel with ascanning direction or portions not irradiated with the laser light 18occur. Because grain growth is disturbed in those portions, it isdesirable to consider a layout design such that no transistor is formedin portions where scanned parts are overlapped with each other. Further,a change occurring to the crystal grains of the polycrystalline siliconthin film upon irradiation thereof with the laser light 18 is aspreviously described.

As with the case of the previously described embodiment, if on the glasssubstrate 1 shown in FIG. 6, transistors requiring fast operation can beput together in either of the driver circuit regions 102, 103, forexample, in the driver circuit region 102, the laser annealing accordingto the invention may be applied to the driver circuit region 102 only.In other words, the active layers (active regions) of the transistorsformed in the driver circuit region 102 are made of polycrystallinesilicon containing crystal grains having no grain boundaries in thedirection of current flow, so that fast operable transistors can beobtained. On the other hand, since thin-film transistors not requiringso fast operation are formed in the driver circuit region 102′, theactive layers (active regions) of the transistors are made up of apolycrystalline silicon film composed of fine crystal grains, simplyannealed by the excimer laser. In this case, since it becomesunnecessary to rotate the substrate or the scanning direction and thedirection of the linear beam, and in addition, regions to be annealedcan be reduced, the effect of improvement in throughput is large.

Or as shown in FIG. 18, if a driver circuit region 602 formed on top ofthe glass substrate 1 can be put together on one side thereof, outsideof a pixel region 601, active layers (active regions) of all thin-filmtransistors of the driver circuit are made up of a polycrystallinesilicon film containing crystal grains having no grain boundaries in thedirection of current flow, so that fast operable transistors can beobtained. In this case as well, it becomes unnecessary to rotate thesubstrate or a scanning direction and the direction of a linear beam, sothat such a configuration is preferable from the viewpoint ofimprovement in throughput. However, a plurality of alignment marks, forexample, alignment marks 603, 603′, shown in the figure, are evidentlyrequired.

Further, with reference to the embodiment previously described, it hasbeen described that the signals from the linear scales (linear encoders)installed in the stage 2 are counted for detecting the position or ashift amount of the stage 2. However, the invention is not limitedthereto, and use may be made of output signals from a measuring machineusing laser light interference, a rotary encoder installed on the axisof a motor driving the stage, and so forth.

Now, there is described hereinafter still another embodiment of aprocess of fabricating a display-device according to the invention. Inthe previously described embodiment, there has been shown a case wherethe annealing regions each approximately 500 μm×100 μm are juxtaposed atthe pitches of 250 μm. Herein, another case where the annealing regionsare juxtaposed at closer pitches is described.

Assuming a case of annealing a region 4 mm in width by scanning withlaser beam 500 μm×10 μm by way of example, an annealing width by onescanning is preferably increased as much as possible within apermissible range of laser output, and an annealing length (a size of anannealing region, in the scanning direction) and a pitch of theannealing region are preferably an integral multiple of a pixel pitch,respectively. In this case, assuming that a pixel pitch is 250 μm, oneannealing region is set to 500 μm×500 μm.

First, regions each 500 μm×500 μm in size are irradiated at pitches of 1mm by a first scanning. In this case, as shown in FIG. 28, therespective regions 500 μm×500 μm are irradiated with laser light, andannealed regions are formed at the pitches of 1 mm. In the respectiveannealed regions 801, 802, 803, there occurs a decrease of filmthickness in regions 811, 812, 813, about 10 μm wide, respectively, ofan anneal start part, due to melted silicon being pulled in the scanningdirection by interfacial tension. In respective regions 821, 822, 823,about 10 μm wide, of an anneal termination part, a swell (protrusion) isformed The respective annealed regions 801, 802, 803, sandwiched betweenthose regions, are well annealed, forming a pseudo-single crystal film,respectively.

Subsequently, by executing annealing at pitches of 1 mm after shiftingan irradiation start position by 500 μm in the scanning direction whilekeeping an irradiation region set at 500 μμm×500 μm as above, regions804, 805, not annealed at the time the precious scanning, are annealed,thereby forming respective annealed regions 500 μm wide as shown in FIG.29. However, as previously described, since film thickness is decreasedor a swell is formed in an irradiation start part and irradiationtermination part, respectively, regions unsuitable for formation oftransistors 811, 842, 843, 844, 845, 823, about 10 μm wide,respectively, are formed at pitches of 500 μm.

Now, dwelling on the region 842, it can be said that this partcorresponds to an anneal termination part at the first scanning and aprotrusion is formed therein, but at the second scanning, this partcorresponds to an anneal start part, so that the protrusion issubstantially eliminated, but is still unsuitable for formation oftransistors in contrast with a normal region, for example, 801. Further,dwelling on the region 843, this part corresponds to an anneal startpart at the first scanning, and film thickness decreases, but this partcorresponds to an anneal termination part at the second scanning and aprotrusion is formed therein, so that this part is unsuitable forformation of transistors.

Next, similar annealing is executed by shifting 500 μm in the directionnormal to the scanning direction, which is repeated until an entirewidth requiring annealing is annealed. With the present embodiment, awidth 4 mm is to be annealed, scanning of 8 rows, that is, scanning isrepeated 16 times.

As shown in FIG. 30, when laser light is irradiated by shifting 500 μmin the direction normal to the scanning direction, in consequence ofsuch operation, irradiation is duplicated, portions not irradiated areleft out, or portions previously irradiated are subjected to thermaleffects at the time of a successive irradiation, thereby disturbingcrystal morphology, in overlapped parts 851, 852. Accordingly, there areleft out the regions 851, 852, unsuitable for formation of transistors.

Having taken those into consideration, it can be said that well annealedregions (that is, pseudo-single crystal regions) each 490 μm×490 μm arefinally formed at pitches of 500 μm as shown FIG. 31. In the interestsof simplicity, it can be said that pseudo-single crystal silicon filmseach 490 μm×490 μm are formed at pitches of 500 μm on the glasssubstrate in such a manner as tiles are stuck thereto. By designing suchthat a transistor can be disposed on the respective tiles ofpseudo-single crystal silicon, high performance transistors can beformed.

Herein, there has been described a case where annealing is executed byscanning in the same direction, however, irradiation may be carried outby setting such that there is a shift of the irradiation position by 500μm between scanning in one direction and scanning in the oppositedirection in the case of reciprocative scanning. In this case, therewill be a change in arrangement of parts with decreased film thicknessand parts with a protrusion, as finally obtained, however, since anythereof is about 10 μm in width, and is unsuitable for formation oftransistors, pseudo-single crystal regions suitable for formation oftransistors will the same as those shown in FIG. 31.

Assuming a case where transistors to be formed are to constitute adriver circuit 981 for signal lines, formed on top of a glass substrate980, as shown in FIG. 35, thee are formed 6 circuits 983 each fordriving 2 pixels at a pitch of 250 μm, more exactly, 2 pixels eachcomprising 1 dot each of R, G, B, that is, 6 dots, in one pseudo-singlecrystal region 982 formed at pitches of 500 μm. Generally, in onepseudo-single crystal region, circuits are formed at identical pitchesto form a circuit group, and these circuit groups are formed at pitchesfor forming the pseudo-single crystal regions. That is, these areconfigured such that, on the glass substrate, the circuits having anidentical function for driving respective signal lines are disposed notat an equal interval throughout one panel, but a plurality of thecircuit groups having an identical function are disposed at identicalpitches.

Assuming a further embodiment where a region 4 mm in width is annealedby scanning with laser beam 500 μm×10 μm by way of example, an annealingwidth by one scanning is preferably increased as much as possible withina permissible range of laser output, and an annealing length (a size ofan annealing region, in the scanning direction) and a pitch of theannealing region are preferably an integral multiple of a pixel pitch,respectively. In this case as well, assuming that a pixel pitch is 250μm, one annealing region is set to 500 μm×500 μm, and irradiation isexecuted at pitches of 500 μm.

First, regions each 500 μm×490 μm in size are irradiated at pitches of 1mm by a first scanning as shown in FIG. 32. In this case, the respectiveregions 500 μm×490 μm are irradiated with laser light, and annealedregions are formed at the pitches of 500 μm. In the respective annealedregions 901, 902, 903, 904, 905, there occurs a decrease of filmthickness in regions 911, 912, 913, 914, 915, about 10 μm wide,respectively, of an anneal start part, due to melted silicon beingcarries away by interfacial tension. In respective regions 921, 922,923, 924, 925, about 10 μm wide, of an anneal termination part, a swell(protrusion) is formed The respective annealed regions 901, 902, 903,904, 905, sandwiched between those regions, are well annealed, forming apseudo-single crystal film, respectively.

Further, with the present embodiment, there is left out a non-irradiatedregion 10 μm wide between the respective irradiation regions, however,these regions are necessary regions in order to temporarily stop crystalgrowth taking place up to then to thereby induce new crystal growth, andalso, to interrupt buildup of heat in the substrate due to laserirradiation.

Next, similar annealing is executed by shifting 500 μm in the directionnormal to the scanning direction, which is repeated until an entirewidth requiring annealing is annealed. With the present embodiment, awidth 4 mm is to be annealed, scanning of 8 rows, that is, scanning isrepeated 16 times.

When laser light is irradiated by changing rows, in consequence of suchoperation, irradiation is duplicated, portions not irradiated are leftout, or portions previously irradiated are subjected to thermal effectsat the time of a successive irradiation, thereby disturbing crystalmorphology, in overlapped parts 951, 952, 953, 954, 955, 956, 957, 958,959, 960. Accordingly, there are left out the regions about 10 μm wide,unsuitable for formation of transistors.

Having taken those into consideration, it can be said that well annealedregions (that is, pseudo-single crystal regions) each 490 μm×470 μm arefinally formed at pitches of 500 μm as shown FIG. 31. In the interestsof simplicity, it can be said that pseudo-single crystal silicon filmseach 490 μm×470 μm are formed at pitches of 500 μm on the glasssubstrate in such a manner as tiles are stuck thereto. By designing suchthat a transistor can be disposed on the respective tiles ofpseudo-single crystal silicon, high-performance transistors can beformed.

Herein, there has been described a case where annealing is executed byscanning in the same direction, however, irradiation may be carried outby setting such that there is a shift of the irradiation position by 500μm between scanning in one direction and scanning in the oppositedirection in the case of reciprocative scanning. In this case, therewill be a change i n arrangement of parts with decreased film thicknessand parts with a protrusion from row to row, however, since any thereofis about 10 μm in width, and is unsuitable for formation of transistors,pseudo-single crystal regions suitable for formation of transistors willthe same as those shown in FIG. 31. In comparison with the previouslydescribed embodiment, the respective pseudo-single crystal regionsbecome slightly narrower, however, throughput is increased about twiceas much.

Assuming a case where transistors to be formed are to constitute adriver circuit 981 for signal lines, formed on top of a glass substrate980, as shown in FIG. 35, thee are formed 6 circuits 983 each fordriving 2 pixels at a pitch of 250 μm, more exactly, 2 pixels eachcomprising 1 dot each of R, G, B, that is, 6 dots, in one pseudo-singlecrystal region 982 formed at pitches of 500 μm. Generally, in onepseudo-single crystal region, circuits are formed at identical pitchesto form a circuit group, and these circuit groups are formed at pitchesfor forming the pseudo-single crystal regions. That is, these areconfigured such that, on the glass substrate, the circuits having anidentical function for driving respective signal lines are disposed notat an equal interval throughout one panel, but a plurality of thecircuit groups having an identical function are disposed at identicalpitches.

In the foregoing description, there has been described that an annealingwidth, annealing length, and a pitch regulate respective laser annealingregions, however, respective sizes can be converted into pulse numbersas generated by the linear scales installed in the stage 2. Accordingly,it is evident that timing for ON/OFF of the laser light can beimplemented by activating at a point in time when corresponding pulsenumbers are counted, respectively. However, detailed description in thisconnection is omitted herein.

FIG. 14 is a schematic representation for illustrating anotherembodiment of an apparatus, that is, a laser annealing apparatus forfabricating the display device according to the invention. The apparatusaccording to the present embodiment comprises a stage 502 on which alarge sized substrate 502 is placed, a plurality of optical body tubes503 each provided with a laser irradiation optical system, adjustmentstages 504 for independently adjusting the respective positions of theoptical body tubes 503, a stand 505 (partly shown in the figure) forholding the adjustment stage 504, continuous-wave oscillators 506, laserdiode power sources 507 for pumping the respective continuous-waveoscillators 506, fibers 508 for transmitting pumped light, and linearscales 509, 510, for detecting the position of the stage 502.

FIG. 15 is a schematic representation for illustrating the opticalsystem in FIG. 14. Inside the respective optical body tubes 503 shown inFIG. 14, there is provided the laser irradiation optical systemcomprising a shutter 511, a beam expander 512, a continuously variabletransmittance filter 513, an EO modulator 514, a cylindrical lens 515, arectangular slit 516, an objective lens 517, a CCD camera 518, and soforth, as shown in FIG. 15. Further, an illuminating light device forobservation, a reference light source a monitor for observation, anautomatic focusing optical system, an image processing device, acontroller, and so forth are omitted in FIG. 15, however, the opticalsystem is basically the same in configuration as that shown in FIG. 1.Further, the respective functions of components are the same as thosefor the annealing apparatus shown in FIG. 1, and detailed descriptionthereof is omitted herein. The present optical system differs from thatin FIG. 1 in that a plurality of (6 in FIG. 14) the laser irradiationoptical systems are housed in the individual optical body tubes(represented by 503 in the figure), respectively, and are fixedlyattached on the adjustment stages (represented by 504 in the figure)capable of independently moving in the directions of X, Y, and Z,respectively, so that the respective positions of the optical body tubes(represented by 503 in the figure) is adjustable so as to enable laserlight to be irradiated to an identical spot on respective panels,thereby enabling laser annealing to be simultaneously applied to aplurality of spots.

Now, there is described a laser annealing method using the laserannealing apparatus described. For a substrate 501, use is made of apolycrystalline silicon thin film substrate 501 obtained by forming anamorphous silicon film on the top surface of a glass substrate 1 shownFIG. 6 through the intermediary of an insulator thin film, and bytransforming the amorphous silicon film into a polycrystalline siliconfilm composed of fine crystal grains after scanning across the amorphoussilicon film with excimer laser light. In this case, the insulator thinfilm is a SiO₂, SiN film, or a composite film thereof. A plurality ofpanels (in FIG. 14, 6 panels on one substrate) is formed on thepolycrystalline silicon thin film substrate.

First, the polycrystalline silicon thin film substrate 501 is placed onthe stage 502. On the polycrystalline silicon thin film substrate 501,alignment marks (not shown) are formed at plural spots of regions wherethe respective panels (in FIG. 14, 6 panels) are to be formed. Thesealignment marks are normally formed by photo-etching techniques,however, use of a photo resist step for this purpose only will result inmuch wastage. Accordingly, after execution of approximate alignment bydetecting the corners of the polycrystalline silicon thin film substrate501, laser light for use in laser annealing is formed in the shape of,for example, a rectangle longer in the longitudinal direction and arectangle longer in the transverse direction, respectively, by use ofthe rectangular slit 516 of the respective optical body tubes 503 tothereby remove portions of the polycrystalline silicon thin film, sothat a cross mark is sequentially formed at plural spots of therespective panels, thereby serving as the alignment marks. Or afterpositioning the respective optical body tubes at a predetermined baseposition, a cross mark may be simultaneously formed at plural spots ofthe respective panels, thereby serving as the alignment marks.Otherwise, dot-like alignment marks may be formed by ink-jet means andso forth.

Subsequently, by taking pictures of the alignment marks at two spotswith the CCD camera 518 of one of the optical body tubes (for example,503), and detecting the position of the center of gravity of therespective pictures, the stage 502 is caused to move along three axes ofX, Y, Z, respectively, according to design coordinates on the basis ofthe alignment marks, thereby implementing fine alignment of thepolycrystalline silicon thin film substrate 501. In this case, the CCDcamera of the optical body tube intended for annealing is used fordetection of the alignment marks, but another optical system foralignment may be installed. In such a case, a plurality of the alignmentmarks may be sequentially detected with one optical system, or aplurality of the alignment marks may be simultaneously detected with aplurality of optical systems.

After completion of alignment of the polycrystalline silicon thin filmsubstrate 501, the stage 502 is moved according to the designcoordinates such that the alignment mark at one spot among the alignmentmarks of the respective panels comes into a field of view of therespective optical body tubes, the pictures of the alignment marks aretaken with the CCD camera 518 of the respective optical body tubes, andadjustment is made with the respective adjustment stages 504 such thatthe center of gravity of the respective pictures coincides with thecenter of the respective fields of view. By so doing, the position ofthe respective optical body tubes is adjusted such that an identicalspot on the respective panels formed on the polycrystalline silicon thinfilm substrate 501 is irradiated with laser light.

Thereafter, as previously described, annealing is applied such that onlya portion of a driver circuit forming region of the respective panels,where an active-layer (active region) is to be formed, is irradiatedwith laser light in accordance with design data. At this point in time,pulse signals generated by the linear scale 509 or 510, installed in thestage 502, are counted and upon the stage 502 reaching the position forirradiation with laser light, the laser light is turned into ON state bythe EO modulator 514, and is condensed into a linear form by thecylindrical lens 515, so that unnecessary portions of the laser lightare cut off by the rectangular slit 516 to be thereby condensed by theobjective lens 517 before irradiation.

Laser energy is adjusted with the continuously variable transmittancefilter 513 as necessary. Further, the signals from the linear scale 509or 510 are counted and when the stage 502 is shifted and passes througha region to be annealed, the laser light is turned into OFF state by theEO modulator 514, so that only regions requiring annealing can beaccurately irradiated with the laser light. Timing for irradiation withthe laser light is as preciously described with reference to FIGS. 7 and13.

Regions to be irradiated with the laser light are, for example, activelayer parts of the thin-film transistors making up the driver circuitfor driving pixels, and while scanning the polycrystalline silicon thinfilm substrate 501 by driving the stage 502, only necessary parts aresequentially irradiated. At this point in time, the respective opticalbody tubes drive the individual adjustment stages 504 with the opticalbody tube mounted thereon in the Z-direction by the agency of anautomatic focusing mechanism (not shown), thereby controlling all theobjective lenses so as to be at a given position in relation to thesurface of the polycrystalline silicon thin film substrate 501.

If a multitude of small sized panels are arranged on one glasssubstrate, a procedure is repeated whereby annealing is executed forevery several panels, and after shifting the glass substrate by adistance corresponding to a pitch at which the panels are arranged,annealing is again executed, thereby enabling all the panels to beannealed. Changes occurring to crystal grains of the polycrystallinesilicon thin film when irradiated with the laser light are as previouslydescribed, and since growth of crystal grain occurs in the direction ofscanning with the laser light, the polycrystalline silicon thin film caneffectively obtain properties equivalent to those of a single crystal bycausing the direction of current flow to coincide with the direction ofcrystal growth when transistors are formed.

Now, a still further embodiment of the invention is describedhereinafter. With the embodiment described in the foregoing, it has beendescribed that only regions to be annealed are irradiated with the laserlight. More specifically, for a time period from the start of movementof the stage 502 until arrival thereof at an irradiation region, thelaser light is kept fully in OFF state and upon the stage 502 reachingthe irradiation region, irradiation is started at a predetermined outputwhile upon the stage 502 passing through the irradiation region, thelaser light is turned fully in OFF state. By repeating such anoperation, laser annealing is applied to a plurality of regions. If thelaser light is irradiated by this method, there occurs the followingphenomenon.

FIG. 20 is a sectional view showing the sectional shape of a thin-filmtransistor substrate to which a laser annealing method according to thepresent embodiment is applied. As shown in FIG. 20, a polycrystallinesilicon thin film 703 formed on a glass substrate 701 through theintermediary of an insulator film 702 melts the instant that irradiationof continuous-wave laser is started at a spot of irradiation start, andmelted silicon is pulled in a scanning direction by the agency ofinterfacial tension. Accordingly, upon cooling and solidification of themelted silicon after passing of the laser light, there occurs a portion705 of the polycrystalline silicon thin film 703, smaller in thickness.In a region following the portion 705 smaller in thickness, a portion704 thereof, having an original film thickness, is maintained, however,when the continuous-wave laser is turned into OFF state at a spot ofirradiation completion, the melted silicon pulled in by the agency ofinterfacial tension cools down and is solidified on the spot, therebycausing a swell 706 to occur.

Thus, the thickness of the silicon film at the spots irradiation startand irradiation completion differs from that in other parts, andconsequently, characteristics of transistors formed at these spots arechanged from those in other parts, so that the transistors cannot bedisposed at these spots. Accordingly, there has been necessity of givingconsideration so as not to allow the portion 705 smaller in thicknessand the swell 706 to overlap the active layer of the respectivetransistors making up the driver circuit. Furthermore, in case the swell706 at the spot of irradiation completion is large, the swell 706 cannotbe completely removed in an etching step for leaving out only the activelayer of the respective transistors, causing etching residue to occur.It has since turned out that there is a problem in that overlyingelectrodes and wiring are broken in the worst case, and reliabilitydeteriorates even if no break occurs thereto. Hence, the following laserirradiation method is adopted.

FIG. 19 is a schematic representation for illustrating a relationshipbetween a stage position according to another embodiment of theinvention and laser output. By changing setting of the EO modulator 10in FIG. 1, laser light is irradiated at low output in a region where noannealing is applied while the laser light is irradiated at high outputin a region where annealing is to be applied as shown in FIG. 19A.Annealing at a power density of the laser light, in a range of 100×10³W/cm² to 500×10³ W/cm², is suitable, however, in the region where noannealing is applied, irradiation is executed at a power density notmore than one third the power density described. FIG. 21 is a sectionalview showing the sectional shape of a thin-film transistor substrate towhich the laser annealing method described with reference to FIG. 19A isapplied.

As shown in FIG. 21, since no annealing is applied to portions of aband-like polycrystalline silicon film 703 formed on a glass substrate701 through the intermediary of an insulator film 702, in regions wherelaser light is irradiated at low output, no damage occurs to thesubstrate, so that an adverse effect of a portion 705′ smaller inthickness at a spot of irradiation start and a swell 706′ at a spot ofirradiation completion, respectively, can be alleviated and in a portionirradiated at output suitable for annealing, growth of crystal grainsoccurs in a direction of scanning with the laser light, therebyobtaining a band-like polycrystalline silicon film of intended filmquality.

Further, as shown in FIGS. 19B or 19C, laser output is successivelyincreased predetermined time or a predetermined distance before reachingan annealing region so as to reach output suitable for annealing uponreaching the annealing region, and after passing through the annealingregion, the laser output is successively decreased so that atpredetermined time or a predetermined distance later, the laser outputbecomes not more than one third the output suitable for annealing or thelaser light is turned into OFF state. As a result, rapid increase intemperature at a spot of irradiation start as well as a spot ofirradiation completion can be eased and an adverse effect of a decreasein thickness at the spot of irradiation start and a swell at the spot ofirradiation completion, respectively, can be alleviated, so that in aportion irradiated at output suitable for annealing, growth of crystalgrains occurs in a direction of scanning with the laser light, therebyobtaining a silicon film of intended film quality.

FIG. 24 is a sectional view of the principal part of a liquid crystaldisplay panel of a liquid crystal display device which is an example ofan embodiment of a display device according to the invention forillustrating an example of configuration thereof. The liquid crystaldisplay panel comprises a first substrate SUB1, a second substrate SUB2,and a liquid crystal layer LC sandwiched in a gap therebetween. Thefirst substrate SUB1 corresponds to the active matrix substrate(thin-film transistor substrate) described with reference to theembodiments in the foregoing. The first substrate SUB1 is a glasssubstrate, and on the top surface, that is, the inner surface thereof,there are formed a gate electrode GT, an active layer (semiconductorfilm) PS1 made up of a band-like polycrystalline silicon film, a sourceelectrode SD1, a drain electrode SD2. And a pixel electrode PX connectedto the source electrode SD1. Further, reference numerals G1, PASD (onelayer or multiplayer) denote insulating layers, OR11 denotes analignment layer, and POL1 a polarizer. On the periphery of the firstsubstrate SUB1, there is formed a driving circuit (driver circuit)described with reference to FIGS. 6 or 18.

Meanwhile, the second substrate SUB2 too is a glass substrate, and onthe top surface (inner surface) thereof, there are formed a color filterCF partitioned with a black matrix BM, an overcoat layer OC, a commonelectrode (opposite electrode) ITO and an alignment layer OR12. Further,reference numeral POL2 denotes a polarizer. An electric field in adirection normal to the surface of the substrate is formed between thepixel electrode PX and the common electrode ITO, and the electric fieldcontrols the direction of the alignment of molecules of liquid crystalcomposition making up the liquid crystal layer in such a way as to allowlight falling on the first substrate SUB1 to go out of the secondsubstrate SUB2 or to block the light, thereby displaying images.

FIG. 25 is a sectional view of the principal part of a liquid crystaldisplay panel of a liquid crystal display device which is an example ofan embodiment of a display device according to the invention forillustrating another example of configuration thereof. The liquidcrystal display panel comprises a first substrate SUB1, a secondsubstrate SUB2, and a liquid crystal layer LC sandwiched in a clearancetherebetween. The first substrate SUB1 corresponds to the active matrixsubstrate (thin-film transistor substrate) described with reference tothe embodiments in the foregoing. The first substrate SUB1 is a glasssubstrate, and on the top surface, that is, the inner surface thereof,there are formed a gate electrode GT, an active layer (semiconductorfilm) PS1 made up of a band-like polycrystalline silicon film, a sourceelectrode SD1, a drain electrode SD2. And pixel electrodes PX connectedto the source electrode SD1, arranged in a manner like the teeth of acomb in a pixel region.

Opposite electrodes CT are interposed between the pixel electrodes PXarranged in the manner like the teeth of the comb.

Further, reference numerals G1, PASD (one layer or multiplayer) denoteinsulating layers, OR11 denotes an alignment layer, and POL1 apolarizer. On the periphery of the first substrate SUB1, there is formeda driving circuit (driver circuit) described with reference to FIGS. 6or 18.

Meanwhile, the second substrate SUB2 too is a glass substrate, and onthe top surface (inner surface) thereof, there are formed a color filterCF partitioned with a black matrix BM, an overcoat layer OC, and analignment layer OR12. Further, reference numeral POL2 denotes apolarizer. An electric field in a direction normal to the surface of thesubstrate is formed between the pixel electrode PX and the commonelectrode ITO, and the electric field controls the direction of thealignment of molecules of liquid crystal composition making up theliquid crystal layer in such a way as to allow light falling on thefirst substrate SUB1 to go out of the second substrate SUB2 or to blockthe light, thereby displaying images.

FIG. 26 is a sectional view for illustrating a schematic configurationof a liquid crystal display device using the liquid crystal displaypanel described with reference to FIGS. 24, and 25.

With the liquid crystal display device (liquid crystal display module),a backlight is installed on the backside of a liquid crystal displaypanel PNL through the intermediary of an optical compensatory sheet OPSmade up of a diffusion sheet laminated to a prism sheet, and a shieldcase SHD, which is an upper case, is formed integrally with a mold caseMDL, which is a lower case. On the periphery of a first substrate SUB1of the liquid crystal panel PNL, there is formed the driving circuit(driver circuit) as described above.

The backlight shown in FIG. 26 is a so-called side lamp type comprisinga light source (herein, a cold cathode fluorescent lamp CFL) disposed onthe side edge of an guide light board GLB suitably made up of an acrylicplate, a reflective sheet RFS, a lamp reflection sheet LFS, and soforth. However, as a backlight other than the type as above, there areknown a so-called directly underside type backlight wherein a pluralityof light sources are disposed directly under the backside of a liquidcrystal display panel, or a so-called front-light type disposed in thevicinity of the surface (visible side) of a liquid crystal displaypanel, and so on.

FIG. 27 is a sectional view of the principal part of a display panelmaking up an organic electro-luminescent display panel, another exampleof the display device according to the invention, for illustrating aschematic configuration thereof. The organic electro-luminescent displaypanel (abbreviated organic EL) comprises a first substrate SUB1, and asecond substrate SUB2, but the second substrate SUB2 is a sealing casefor protecting various function films of the first substrate SUB1, asdescribed hereinafter, from environments, and is made up of not only aglass substrate but also a metal sheet at times. The first substrateSUB1 corresponds to the active matrix substrate (thin-film transistorsubstrate) described with reference to various embodiments in theforegoing. The first substrate SUB1 is a glass substrate, and on the topsurface, that is, inner surface thereof, there are provided thin-filmtransistors made of the band-like polycrystalline silicon film asreformed by the previously described method.

Respective pixel circuits of the organic EL panel have at least thethin-film transistors for switching and the thin-film transistors fordriving, and the thin-film transistors shown in the figure correspond tothe thin-film transistors for driving, the thin-film transistors forswitching being omitted in the figure. The thin-film transistorcomprises a band-like polycrystalline silicon film PS1, a gate electrodeGT, and a source electrode SD. Further, it comprises an anode ADconnected to the source electrode SD, a luminescent layer OLE, and acathode CD. Reference numerals IS (IS1, IS2, IS3), PSV, IL denote aninsulating layer, respectively. There is a case where a desiccant isprovide on the inner surface of the second substrate SUB2. Further,dispositions of the anode AD and cathode CD are not necessarily limitedto those shown in the figure, and respective polarities may be changedover.

With this configuration, current flows between the anode AD and cathodeCD by selection of the thin-film transistors for driving, whereupon theluminescent layer OLE, interposed between the anode AD and cathode CD,emits light. The emitted light outgoes from the side of the firstsubstrate SUB1. There is another type wherein reflective metal is usedfor the anode AD, and a transparent electrode is used for the cathodeCD, thereby sending out the emitted light from the side of the secondsubstrate SUB2 In such a case, a transparent sheet such as a glass sheetis used for the second substrate SUB2 (sealing case). The organic ELpanel is housed in an appropriate case or frame to be used as an organicEL display device (module).

It is to be pointed out that the invention is not limited to thoseconfigurations as described hereinbefore, and that various changes andmodifications may be made in the invention without departing from thespirit and scope thereof. Further, it is obvious that the invention issimilarly applicable to a substrate for various electronic equipmentwherein active elements such as thin-film transistors are formed on aninsulating substrate.

As described hereinbefore, with the process (laser annealing method) offabricating the display device according to the invention and theapparatus (laser annealing apparatus) for fabricating the same, laserlight can be accurately irradiated to a spot to be irradiated (annealed)without variation in stage speed while preventing adverse effects on theinsulating substrate such as a glass substrate. Further, since the stagemoves at a constant speed, annealing can be executed under a constantcondition regardless of the position of a spot on the substrate.

As a result, by causing growth of crystal grains of the amorphous orpolycrystalline silicon thin film to take place in a desired direction,these can be reformed into the band-like polycrystalline silicon filmcomposed of large crystal grains in excess of 10 μm in grain size, sothat mobility of the active elements such as the thin-film transistors,made of the band-like polycrystalline silicon film, can be drasticallyimproved.

The active elements such as the thin-film transistors, formed of asilicon film reformed by the process of the invention, have performancesufficient for making up the driver circuit in a display device such asa liquid crystal display device, an organic EL display, so that a systemon panel can be implemented, and various display devices for a liquidcrystal display device intended for reduction in size and cost.

While we have shown and described several embodiments in accordance withour invention, it should be understood that disclosed embodiments aresusceptible of changes and modifications without departing from thescope of the invention. Therefore, we do not intend to be bound by thedetails shown and described herein but to intend to cover all suchchanges and modifications as fall within the ambit of the appendedclaims.

1. An apparatus for fabricating a display device, comprising: a stage capable of mounting an insulating substrate of the display device and moving the insulating substrate; at least one position sensor which detects at least one of a position and moving distance of the substrate; a laser oscillator which generates continuous-waves laser light; a modulator which turns ON/OFF the continuous-wave laser light generated by the laser oscillator; a beam forming optic which shapes the continuous-wave laser light passing through the modulator into at least one of a linear and rectangular form; an objective lens which projects the at least one of linear and rectangular laser light on the insulating substrate so as to irradiate the insulating substrate with the at least one of linear and rectangular laser light; and a controller which counts signals generated by the at least one position sensor for every movement of the stage for a given distance, which causes the modulator to turn the generated continuous-wave laser light in an ON state at time when a position of the insulating substrate on which the laser light irradiation is to be started reaches an area on which the at least one of linear and rectangular laser light is projected, and which causes the modulator to turn the generated continuous-wave laser light in an OFF state at time when another position of the insulating substrate on which the laser light irradiation is to be stopped reaches the area; wherein a plurality of regions on the substrate are irradiated with the continuous-wave laser light in a state when the substrate is kept in continuous movement.
 2. An apparatus for fabricating a display device according to claim 1, wherein the modulator is an electro-optical modulator.
 3. An apparatus for fabricating a display device according to claim 1, wherein the insulating substrate is a substrate with an amorphous semiconductor film of a granular polycrystalline semiconductor film formed thereon.
 4. An apparatus for fabricating a display device according to claim 1, wherein the continuous-wave laser light is light of a second harmonics of a laser diode pumped YVO₄ continuous wave laser.
 5. An apparatus for fabricating a display device according to claim 1, wherein a plurality of laser oscillators, a plurality of modulators, a plurality of beam forming optics, and a plurality of objective lenses are provided; and wherein a plurality of spots on the insulating substrate which is mounted on the stage are simultaneously irradiated with the laser light.
 6. An apparatus for fabricating a display device, comprising: a stage capable of mounting an insulating substrate of the display device and moving the insulating substrate; at least one position sensor which detects at least one of a position and moving distance of the substrate; a laser oscillator which generates continuous-wave laser light; a modulator which turns ON/OFF the continuous-wave laser light generated by the laser oscillator; a beam forming optics which shapes the continuous-wave laser light passing through the modulator into at least one of a linear and rectangular form; an objective lens which projects the at least one of linear and rectangular laser light on the insulating substrate so as to irradiate the insulating substrate with the at least one of linear and rectangular laser light; and a controller which counts signals generated by the at least one position sensor for every movement of the stage for a given distance, which causes the modulator to turn the generated continuous-wave laser light in an ON state at time when a position of the insulating substrate on which the laser light irradiation is to be started which reaches an area on which the at least one of linear and rectangular laser light is projected, and which causes the modulator to turn the generated continuous-wave laser light in an OFF state at time when a preset time has elapsed from the start of the laser light irradiation; and wherein a plurality of regions on the substrate are irradiated with the continuous-wave laser light in a state when the substrate is kept in continuous movement.
 7. An apparatus for fabricating a display device according to claim 1, wherein the at least one position sensor includes a plurality of linear scales, each of the linear scales being installed in the stage.
 8. An apparatus for fabricating a display device according to claim 1, wherein the at least one position sensor includes a plurality of measuring machines, each of the measuring means enabling measurement using laser light interference.
 9. An apparatus for fabricating a display device according to claim 1, wherein the at least one position sensor includes a plurality of rotary encoders, each of the rotary encoders being installed on an axis of a motor which drives the stage.
 10. An apparatus for fabricating a display device according to claim 6, wherein the at least one position sensor includes a plurality of linear scales, each of the linear scales being installed in the stage.
 11. An apparatus for fabricating a display device according to claim 6, wherein the at least one position sensor includes a plurality of measuring machines, each of the measuring means enabling measurement using laser light interference.
 12. An apparatus for fabricating a display device according to claim 6, wherein the at least one position sensor includes a plurality of rotary encoders, each of the rotary encoders being installed on the axis of a motor driving the stage. 